The invention relates to a pseudo-substrate for use in the production of semiconductor components, and to a method for producing such a pseudo-substrate.
Semiconductor components, in particular for telecommunications and for high-speed applications, are typically produced by applying various layers onto substrates.
One essential criterion for the substrates used is in this case the lattice constant, which should be matched to the lattice constant of the layers to be applied. Often, however, corresponding substrates having the desired lattice constant are not available, or are not available with a sufficient quality, size or cost.
It is therefore known to employ pseudo-substrates for the crystal growth of layers for producing semiconductor components. In this case, commercially available substrates are typically used, for example Si or GaAs substrates, on which non-lattice-matched (metamorphic) and therefore defect-richer layers are deposited. With suitable process management and a sufficient layer thickness, a low-defect surface is thereby formed with a lattice constant different to that of the substrate. This newly generated surface is then used as a substrate for the growth of the layers of the actual component. For example, the use of GaAs substrates on which a metamorphic buffer layer consisting of indium, gallium and arsenic is applied in order to match the lattice constant is known, and described in Kenneth E. Lee, Eugene A. Fitzgerald, “High-quality metamorphic compositionally graded InGaAs buffers”, Journal of Crystal Growth 312 (2010) 250-257.
The aforementioned pseudo-substrates are employed particularly in the production of HEMTs (High Electron Mobility Transistors) and MMIC (Monolithic Microwafe Integrated Circuits). To this end, a use of the aforementioned buffer layers for producing a pseudo-substrate has already been described in A. Leuther, A. Tessmann, H. Massler, R. Loesch, M. Schlechtweg, M Mikulla, O. Ambacher, “35 nm Metamorphic HEMT MMIC Technology”, Proc. 20th Int. Conf. On Indium Phoshide and Related Materials, May 2008, paper MoA3.3″ and A. Leuther, R. Weber, H. Dammann, M Schlechtweg, M Mikulla, M Walther, G. Weimann, “Metamorphic 50 nm InAs-channel HEMT”, Proc. 17th Int. Conf On Indium Phoshide and Related Materials, 2005, p. 129-132.
Since pseudo-substrates in principle have flaws and therefore defects inside the buffer layers, the risk arises that undesired electrical or optical properties, which restrict or exclude usability of the pseudo-substrates, will be induced in the event of an excessively high defect density. For example, in the event of a large lattice mismatch and a high defect density resulting therefrom, defect bands may be formed which influence the electrical and optical properties of the semiconductor component. In particular, an electrical conductivity resulting from the defect bands can render the pseudo-substrate unsuitable for radiofrequency applications.